1. Field of the Invention
The present invention relates to an optical data storage medium comprising a reflective layer having thereon a print made by utilizing the metallic gloss and light diffraction of the reflective layer thereof.
2. Description of the Related Art
Optical data storage media for use in recording and reproduction by means of laser light or the like are called optical disks, and among optical disks, compact disks which are used for audio reproduction are well known. A compact disk comprises a plastic transparent substrate having thereon spiral pits formed by injection molding, and a reflective layer which is made of a metal and provided on the substrate. The information is read by illuminating with laser light the disk as it rotates.
In recent years, an write-once type recordable optical data storage medium has also been put to practical use. The write-once type recordable optical data storage medium comprises a plastic transparent substrate, and a recordable layer and a reflective layer provided on the substrate in that order. Recording of information is performed by utilizing a physical or chemical change of the recordable layer which is caused by the irradiation with laser light, and reading out of the recorded information is also performed by the irradiation with laser light. On these optical disks, grooves in spirals having a narrow pitch width are provided by injection molding for the purpose of tracking the laser light for recording/reproduction.
Since an optical disk has in the inside thereof a reflective layer made of a highly reflective metal, the optical disk has a metallic gloss when viewed from the exterior. Further, since the light-diffracting effect due to the spiral pits or grooves causes the light to be reflected in angular directions corresponding to wavelengths, the optical disk has iridescent shimmer depending on the angle at which it is viewed.
However, in the case of a commercially available optical disk, a label or the like is already printed on the front surface, and ink such as a pigment-based ink, which has a high light-diffusing effect, is used in the printing. Consequently, in a conventional optical disk, only the side on which the recording/reproducing light is incident has the above-mentioned iridescent shimmer. Therefore, it has not been possible to utilize, as a feature of the external appearance, the peculiar reflection characteristics inherent to the structure of the optical disk.
With the foregoing in view, an object of the present invention is to provide an optical data storage medium having an excellent visual effect by utilizing, but not impairing, the metallic gloss and light-diffraction-based iridescent reflection characteristics caused by a reflective layer provided on a substrate having concavities and convexities.
After intense studies, the present inventors found that the application of transparent coloring ink such that the regular reflectance of the front surface of an optical disk falls within a specific range does not impair the metallic gloss and the iridescent reflection characteristics which is caused by light diffraction. Based on this discovery, the present inventor achieved the present invention.
The optical data storage medium of the present invention comprises: a substrate having thereon concavities and convexities so that diffraction of reflected light is caused; a reflective layer provided on the side of the substrate which side has the concavities and convexities; and a colored region which is provided by applying a transparent coloring ink to at least a region of the reflective layer, the regular reflectance in the colored region with respect to light incident from the side opposite to the substrate side being within a range of from 3 to 80%.
In another aspect of the presennt inventions, the optical data storage medium comprises: a substrate having thereon concavities and convexities so that diffraction of reflected light is caused; a reflective layer provided on the side of the substrate which side has the concavities and convexities; a protective layer provided on the reflective layer; and a colored region which is provided by applying a transparent coloring ink to at least a region of the protective layer, the regular reflectance in the colored region with respect to light incident from the side opposite to the substrate side being within a range of from 3 to 80%.
Average regular reflectance of the colored region with respect to light incident from the side opposite to the substrate side and having wavelengths ranging from 400 to 700 nm is preferably 10% or more.
The concavities and convexities are preferably formed by grooves which are provided in concentric circles and have an average pitch of 0.1 to 50 xcexcm and an average depth of 10 to 5000 nm.
The regular reflectance in the colored region with respect to light incident from the side opposite to the substrate side can be controlled by controlling the coating amount of the transparent coloring ink. Further, the wavelength spectrum of the light reflected in the colored region with respect to light incident from the side opposite to the substrate side can be controlled by changing the absorption of the transparent coloring ink. It is also possible to control the wavelength spectrum of the light reflected in the colored region with respect to light incident from the side opposite to the substrate side by using as the transparent coloring ink two or more transparent coloring inks each having different absorption and applying the transparent coloring inks as plural coast.
It is preferable that a UV-curable ink is used as the transparent coloring ink.
In yet another aspect of the present inventions, the optical data storage medium comprises: a substrate having thereon concavities and convexities so that diffraction of reflected light is caused; a recording layer which is writable by light and which is provided on the side of the substrate which side has the concavities and convexities; a reflective layer provided on the recording layer; and a colored region which is provided by applying a transparent coloring ink to at least a region of the reflective layer, the regular reflectance in the colored region with respect to light incident from the side opposite to the substrate side being within a range of from 3 to 80%.
It is preferable that recording layer is a recording layer based on a dye.